A solid-state image pickup device has photosensitive elements aligned in one dimension or two dimensions and can take a one-dimensional or two-dimensional optical image by converting the intensity of light that is incident on each of the photosensitive elements to an electrical signal and outputting this electrical signal. A solid-state image pickup device is used, for example, in a facsimile machine to read an image on a manuscript or to take an image formed by X-rays that have been transmitted through an inspected object in a non-destructive X-ray inspection device. It is demanded that such a solid-state image pickup device takes an image with high speed.
For example, a solid-state image pickup device disclosed in Japanese Unexamined Patent Publication No. Hei-10-126696 comprises: a photoelectric conversion circuit, converting an optical signal to a voltage and outputting this voltage; a VI conversion circuit, converting the voltage output from the photoelectric conversion circuit to a current and outputting this current; and an IV conversion circuit, converting the current output by the VI conversion circuit to a voltage and outputting this voltage. The respective output terminals of a plurality of VI conversion circuits are selectively and successively connected to a single IV conversion circuit.
With a solid-state image pickup device arranged thus, current is transmitted from a VI conversion circuit disposed at a prior stage to the IV conversion circuit disposed at a subsequent stage and the potential at the input terminal of the IV conversion circuit at the subsequent stage is fixed. Thus with this solid-state image pickup device, even if the parasitic capacitance across the respective output terminals of the plurality of VI conversion circuits and the input terminal of the IV conversion circuit is large, the processing of signals among these components can be performed at high speed and image taking can thus be performed at high speed.